Fuel injection valve

ABSTRACT

A fuel injector, in particular a high pressure injector for direct injection of fuel into a combustion chamber of an internal combustion engine having externally supplied ignition and mixture compression, is characterized in that a valve needle, which is movable axially along a longitudinal axis of the valve, has a specially designed valve closing section on its downstream end. To open and close the valve, the valve closing section works together with a fixed valve seat. Swirl-producing elements are arranged upstream from the valve seat while a flattened face running perpendicular to the longitudinal axis of the valve is provided on the downstream end of the valve closing section downstream from the valve seat.

FIELD OF THE INVENTION

The present invention relates to a fuel injector according to presentinvention.

BACKGROUND INFORMATION

An electromagnetic ally operated fuel injector is described in GermanPublished Patent Application No. 38 08 635, which describes a valveclosing section designed on an axially movable valve needle to worktogether with a fixed valve seat for opening and closing the valve. Thevalve closing section is designed with a conical shape narrowing in thedownstream direction, while the valve seat has the form of a truncatedcone. This valve closing section forms the downstream end of the valveneedle which tapers to a conical tip. Upstream from the valve closingsection and the valve seat, the valve needle is provided with aplurality of spiral-shaped fuel channels through which fuel to beinjected reaches the valve seat with a swirl to improve fuel atomizationand control the fuel flow rate.

In addition to the conically tapered downstream tip of the valve needle,U.S. Pat. No. 5,350,119 describes a fuel injector having an axiallymovable valve needle with a rounded valve closing section forming thedownstream end of the valve needle.

In addition, German Patent No. 30,46 889 describes a fuel injectorhaving a flat armature and a valve closing part attached thereto. Thismovable valve member works together with a valve seat rigidly connectedto the housing. The closing part has a convex valve closing sectionsealed by a flat polished section running perpendicular to thelongitudinal axis of the valve. Downstream from the valve seat is acollecting space whose volume should be as small as possible and whichis delimited by the valve seat body, the flat lower end of the valveclosing section and the opposite planar upper bordering face of a swirlbody arranged downstream from the valve seat body. Each swirl body has aplurality of swirl channels beginning at the side of the swirl body andopening into a central swirl chamber.

Japanese Laid Open Patent Application No. 10047210 describes a fuelinjector for a fuel injection system of an internal combustion engine,where the fuel injector has an energizable actuating element and a valveneedle that is movable axially along a longitudinal axis of the valveand has on its downstream end a valve closing section which workstogether with a fixed valve seat to open and close the valve. The valveseat is designed on a flat valve seat element. Upstream from the valveseat, the valve has a swirl body which functions as a guide for thevalve needle and also produces a swirl in the fuel spray. Downstreamfrom the valve seat, a flattened face running perpendicular to thelongitudinal axis of the valve is provided on the downstream end of thevalve closing section. The valve seat is followed by an outlet orificehaving a diameter D which is much greater than the diameter of theflattened face formed on the valve needle.

SUMMARY OF THE INVENTION

The fuel injector according to the present invention has the advantagethat improved fuel preparation is achieved upstream from the valve seatin comparison with known valves in that a swirl is produced in the fuel.In particular, the improved quality of fuel preparation concerns theprestream. This prestream is formed by fuel which collects in an innerswirl chamber of the swirl-producing elements in front of the valve seatwhen the valve is closed. When the valve opens, most of this fuel flowslargely axially and without a swirl toward an outlet orifice arrangeddownstream from the valve seat. The measures according to the presentinvention effectively allow better preparation of fuel in the prestreamby making use of the fact that the starting flow which forms theprestream and the development of a wall film in the outlet orifice canbe influenced to a great extent by the design of the valve needle tipwhich contributes to forming the flow region of the spiral flow. Dropletsize can be reduced by the method according to the present invention,thus producing a finer fuel spray. The energy loss by the fuel on theflattened surface of the valve needle reduces the extent of theprestream, which tends to be harmful. In comparison with valve needleshaving a tapered point or a rounded end, a shortened prestream havinglower penetration is advantageously achieved.

In addition, increased homogeneity of the subsequent swirling mainstream can be achieved in comparison with valve needles having a taperedpoint or a rounded end.

It is especially advantageous if, given a known size of the outletorifice having diameter D, diameter d of the flattened area formed onthe downstream end of the valve needle is selected so that ratio d/Damounts to approx. 1.5.

The swirl-producing elements are advantageously designed as disk-shapedswirl elements having a very simple structure which is thus easilymolded. In comparison with swirl bodies having grooves or similarswirl-producing recesses on an end face, an inner opening area can becreated with the simplest expedient in the swirl element, extending overthe entire axial thickness of the swirl element and surrounded by anouter peripheral edge area.

Like the swirl element and the valve seat element, the guide element canalso be easily manufactured. It is especially advantageous that theguide element having an inner guide orifice functions as a guide for thevalve needle traversing it. In one design of the guide element havingalternating projecting areas in the form of teeth with recesses betweenthem on the outer periphery, it is possible to guarantee optimum flowinto the swirl channels of the swirl element underneath in a simple way.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first embodiment of a fuel injector.

FIG. 2 shows a second example of a fuel injector, showing only thedownstream valve end.

FIG. 3 shows a first guide area and seat area as an enlarged detail fromFIG. 2.

FIG. 4 shows a second guide area and seat area.

FIG. 5 shows a third guide area and seat area.

FIG. 6 shows a part of a valve needle end having a different geometry incomparison with the preceding embodiment.

FIG. 7 shows a swirl element.

FIG. 8 shows a guide element which can be used in fuel injectorsaccording to FIGS. 1 through 5.

DETAILED DESCRIPTION

The electromagnetically operated valve shown in FIG. 1 as an example ofan embodiment in the form of an injection valve 13 for the fuelinjection system 12 of an internal combustion engine with externallysupplied ignition has a tubular, largely hollow cylindrical core 2 whichis at least partially surrounded by a solenoid coil 1 and functions asan internal pole of a magnetic circuit. The fuel injector that isillustrated in FIG. 1 is especially suitable as a high-pressureinjection valve for direct injection of fuel into the combustion chamber10 of an internal combustion engine 11 and is configured for a directinjection of a fuel into a combustion chamber 10 of and internalcombustion engine 11. A stepped coil body 3 made of plastic, forexample, holds a winding of solenoid coil 1 and permits an especiallyshort and compact design of the injection valve in the area of solenoidcoil 1 in combination with core 2 and a toroidal, nonmagneticintermediate part 4 having an L-shaped cross section partiallysurrounded by solenoid coil 1.

A longitudinal through orifice 7 is provided in core 2, extending alonga longitudinal axis 8 of the valve. Core 2 of the magnetic circuit alsofunctions as a fuel inlet connection, longitudinal orifice 7 forming afuel feed channel. An outer metallic (e.g., ferritic) housing part 14fixedly connected to core 2 above solenoid coil 1 closes the magneticcircuit as an external pole or an external conducting element andcompletely surrounds solenoid coil 1 at least in the peripheraldirection. A fuel filter 15 is provided in longitudinal orifice 7 ofcore 2 at the inlet end to filter out fuel components whose size mightcause blockage or damage in the injector. Fuel filter 15 is secured incore 2 by pressing, for example.

Core 2 together with housing part 14 forms the inlet end of the fuelinjector, upper housing part 14 extending axially downstream, forexample, beyond solenoid coil 1. Upper housing part 14 is connectedtightly and rigidly to a lower tubular housing part 18 which surroundsand accommodates an axially movable valve part composed of an armature19 and a rod-shaped valve needle 20, i.e., an elongated valve seatcarrier 21. Two housing parts 14 and 18 are rigidly connected by aperipheral weld, for example.

In the embodiment illustrated in FIG. 1, lower housing part 18 and valveseat carrier 21, which is largely tubular, are joined fixedly togetherby screwing; however, welding, soldering or crimping are other possiblejoining methods. A seal is produced between housing part 18 and valveseat carrier 21 by a sealing ring 22, for example. Over its entire axialextent, valve seat carrier 21 has a continuous inner orifice 24 which isconcentric with longitudinal axis 8 of the valve.

At its lower end 25, which also forms the downstream closure of theentire fuel injector, valve seat carrier 21 surrounds a disk-shapedvalve seat element 26 which fits into through hole 24 with a valve seatface 27 tapering in the form of a truncated cone downstream. Rod-shapedvalve needle 20 having a mostly circular cross section is arranged inthrough hole 24 and has a valve closing section 28 on its downstreamend. This valve closing section 28, which is spherical or partiallyspherical or rounded or has a conical taper, works together with valveseat face 27 provided in valve seat element 26 in a known manner. Valveclosing section 28 as the downstream end of valve needle 20 endsdownstream with a flattened face 29 which is designed to be flataccording to the present invention and runs perpendicular tolongitudinal axis 8 of the valve. Flattened face 29 is, for example, aflat polished section. Downstream from valve seat face 27, at least oneoutlet orifice 32 for the fuel is provided in valve seat element 26.

The injector is operated electromagnetically in a known way. However, apiezoactuator or a magnetostrictive actuator is also conceivable as anenergizable actuating element. Likewise, actuation by a controlledpressure-loaded piston is also conceivable. The electromagnetic circuithaving solenoid coil 1, core 2, housing parts 14 and 18 and armature 19is responsible for the axial movement of valve needle 20 and thus foropening the injector against the spring force of a restoring spring 33arranged in longitudinal orifice 7 of core 2 and for closing theinjector. Armature 19 is connected by a weld, for example, to the end ofvalve needle 20 facing away from valve closing section 28 and is alignedwith core 2. A guide opening 34 in valve seat carrier 21 on the endfacing armature 19 and also a disk-shaped guide element 35 having anaccurately dimensioned guide opening 55 arranged upstream from valveseat element 26 are provided for guiding valve needle 20 during itsaxial movement with armature 19 along longitudinal axis 8 of the valve.Armature 19 is surrounded by intermediate part 4 during its axialmovement.

Another disk-shaped element, namely a swirl element 47, is arrangedbetween guide element 35 and valve seat element 26, so that all threeelements 35, 47 and 26 sit directly one on the other and areaccommodated in valve seat carrier 21. Three disk-shaped elements 35, 47and 26 are fixedly joined together by material bonding, for example.

An adjusting sleeve 38 which is inserted, pressed or screwed intolongitudinal orifice 7 of core 2 is used to adjust the spring prestressof restoring spring 33, which is in contact with adjusting sleeve 38over a centering piece 39 on its upstream end and is supported onarmature 19 on its opposite end. Armature 19 has one or more bore-likeflow channels 40 through which fuel can flow into through hole 24 fromlongitudinal orifice 7 in core 2 by passing through connecting channels41 downstream of flow channels 40 near guide opening 34 in valve seatcarrier 21.

The lift of valve needle 20 is predetermined by the installed positionof valve seat element 26. When solenoid coil 1 is not energized, one endposition of valve needle 20 is defined by valve closing section 28coming in contact with valve seat face 27 of valve seat element 26,while the other end position of valve needle 20 when solenoid coil 1 isenergized is determined by armature 19 coming in contact with thedownstream end face of core 2. The surfaces of the parts in the latterstop area may be chrome plated, for example.

Electric contacting of solenoid coil 1 and thus its energization areaccomplished over contact elements 43 which are provided with a plasticsheathing 44 outside of coil body 3. Plastic sheathing 44 may extendover additional parts (e.g., housing parts 14 and 18) of the fuelinjector. An electric cable 45 supplying electric power to solenoid coil1 extends out of plastic sheathing 44. Plastic sheathing 44 projectsthrough upper housing part 14, which is interrupted in this area.

FIG. 2 shows a second embodiment of a fuel injector, showing only thedownstream end of the valve. In contrast with the example shown in FIG.1, several connecting channels 41 running in parallel to the valve axisare provided in valve seat carrier 21 in the area of guide opening 34.To permit reliable influx into valve seat carrier 21, through hole 24 isdesigned to have a larger diameter, while valve seat carrier 21 isdesigned to have a thinner wall.

FIG. 3 shows the guide area and seat area as a detail from FIG. 2 on anenlarged scale to better illustrate this valve area, where the end ofthe valve needle is designed according to the present invention. Theguide area and seat area provided in spray end 25 of valve seat carrier21 in its through hole 24 is formed in the embodiment illustrated inFIG. 3 by three axially successive disk-shaped elements having separatefunctions that are fixedly linked together.

Guide element 35, very flat swirl element 47 and valve seat element 26are provided one after the other in the downstream direction.

Valve seat element 26 may have an outside diameter such that it can fittightly with a small clearance in a lower section 49 of through hole 24in valve seat carrier 21 downstream from a step 51 provided in throughhole 24. Guide element 35 and swirl element 47 have a slightly smalleroutside diameters than valve seat element 26, for example.

Guide element 35 has a dimensionally accurate inside guide orifice 55through which valve needle 20 moves during its axial movement. Guideelement 35 has several recesses 56 distributed over its outercircumference, guaranteeing fuel flow along the outer circumference ofguide element 35 into swirl element 47 and further in the direction ofvalve seat face 27. An embodiment of swirl element 47 and an embodimentof guide element 35 are described in greater detail with reference toFIGS. 7 and 8.

The three elements 35, 47 and 26 are in direct contact at theirrespective end faces and are fixedly joined together before beingassembled in valve seat carrier 21. The fixed connection of individualdisk-shaped elements 35, 47 and 26 is accomplished through materialbonding or welding as preferred joining methods on the outercircumference of elements 35, 47, 26. In the example shown in FIG. 3,weld spots or short welds 60 are provided in the circumferential areaswhere guide element 35 has no recesses 56. After three elements 35, 47,36 are joined, guide opening 55, valve seat face 27 and top end face 59of guide element 35 are ground in a clamp. Thus, these three faces havea very low radial eccentricity relative to one another.

The entire multi-disk valve body is inserted into through hole 24 untiltop end face 59 of guide element 35 is in contact with step 51. Thevalve body is secured by a weld 61 produced by a laser, for example, onthe lower end of the valve between valve seat element 26 and valve seatcarrier 21.

According to the present invention, the downstream end of valve closingsection 28 and thus also of the entire valve needle 20 are provided withflattened face 29 running perpendicular to longitudinal axis 8 of thevalve. Flattened face 29 provided on valve needle 20 has a diameter dwhich is greater than diameter D of outlet orifice 32 downstream, sothat d>D. It is especially advantageous if diameter d is selected whenthe size of outlet orifice 32 is known so that ratio d/D is approx. 1.5.When swirl is produced upstream of valve seat face 27, two successivetypes of stream are formed when the valve is opened by the lifting ofvalve closing section 28 from valve seat face 27. When the valve opens,first a prestream enters outlet orifice 32. This prestream is formed byfuel that has collected in an inner swirl chamber 92 of swirl element 47upstream from the valve seat when the valve is closed. When the valveopens, this fuel flows mostly axially and without a swirl toward outletorifice 32. Only directly after this follows the actual main streamformed by fuel which has flowed through swirl element 47 immediatelyprior to that and therefore has a swirl.

Flattened face 29 on valve needle 20 then causes improved preparation ofthe prestream in an advantageous manner, because flattened face 29permits a preliminary turbulence in the fuel. Droplet size can bereduced in this way, resulting in a finer fuel spray. In addition,greater homogeneity of the main stream in comparison with valves havinga tapered or rounded end can be achieved in this way. It should bepointed out explicitly that the design of swirl element 47 arrangedupstream from valve seat 27 is irrelevant for the present invention.Instead of disk-shaped swirl element 47 shown here, swirl-producingelements of any desired design (e.g., cylindrical swirl bodies, swirlgrooves on the valve needle) may also be used.

In the other embodiments in the following figures, parts that are thesame or have a similar effect to those in the embodiment in FIGS. 2 and3 are indicated with the same reference numbers. The main differencesinclude the design of outlet orifice 32 in valve seat element 26 and themounting of valve seat element 26 on valve seat carrier 21, but not thedesign of the end of the valve needle according to the presentinvention.

As illustrated in FIG. 3, a projection of the flattened face 29 in adirection perpendicular to entry plane 110 completely covers entry plane110.

In the example shown in FIG. 4, valve seat element 26 has a peripheralflange 64 which grips under the downstream end of valve seat carrier 21.Top side 65 of peripheral flange 64 is ground with guide opening 55 andvalve seat face 27 in a clamp. The three-disk valve body is inserteduntil coming in contact with top side 65 of flange 64 at end 25 of valveseat carrier 21. Both parts 21 and 26 are welded together in thiscontact area. Outlet orifice 32 is introduced at an inclination tolongitudinal axis 8 of the valve, ending downstream in a convex sprayarea 66.

The example shown in FIG. 5 corresponds essentially to the example inFIG. 4, the main difference being that an additional fourth disk-shapedspray element 67 is provided here in the form of a spray hole diskhaving outlet orifice 32. Thus in comparison with FIG. 4, valve seatelement 26 is divided again downstream from valve seat face 27. Sprayelement 67 and valve seat element 26 are fixedly joined by a weld 68produced by laser welding, for example, with the welding performed in anannular peripheral recess 69. In addition to laser welding, bonding andresistance welding are suitable joining methods for this joint. In thearea of top side 65′ of spray element 67 and end 25 of valve seatcarrier 21, the two parts are joined fixedly (weld 61).

To prevent wear, valve seat element 26 has a high carbon content and ishighly tempered, making it less weldable. Spray element 67, however, ismade of a more weldable material. Furthermore, weld 68 need have only alow load bearing capacity. Outlet orifice 32 can be producedinexpensively late in the manufacturing process by drilling, forexample. At the entrance to outlet orifice 32 there is a sharp hole edgewhich produces turbulence in the flow, resulting in atomization in veryfine droplets.

FIG. 6 illustrates a valve needle end, shown partially here, having adifferent geometry in comparison with the previous embodiments. In theexample illustrated in FIG. 6, d<D, i.e., flattened face 29 provided onthe downstream end of valve needle 20 has a diameter d smaller thandiameter D of outlet orifice 32 which follows on the downstream end. Adefined breakaway of flow, which may be desirable for certainapplications, can also be achieved with such a design.

FIG. 7 shows a top view of a swirl element 47 embedded between guideelement 35 and valve seat element 26 as a single part. Swirl element 47can be produced inexpensively from sheet metal by punching, wireerosion, laser cutting, etching or other known methods or by galvanicdeposition. An internal opening area 90 running over the entire axialthickness of swirl element 47 is provided in swirl element 47. Openingarea 90 is formed by an inner swirl chamber 92 through which valveclosing section 28 of valve needle 20 extends and by a plurality ofswirl channels 93 opening into swirl chamber 92. Swirl channels 93 opentangentially into swirl chamber 92, and their ends 95 facing away fromswirl chamber 92 are not connected to the outer circumference of swirlelement 47. Instead, a peripheral edge area 96 remains between ends 95of swirl channels 93, which are designed as inlet pockets, and the outerperiphery of swirl element 47.

With valve needle 20 installed, swirl chamber 92 is delimited on theinside by valve needle 20 (valve closing section 28) and on the outsideby the wall of opening area 90 of swirl element 47. Due to thetangential opening of swirl channels 93 into swirl chamber 92, arotational momentum is imparted to the fuel and is maintained in theremaining flow as far as outlet orifice 32. Due to centrifugal force,fuel is sprayed in the form of a hollow cone. Ends 95 of swirl channels93 function as collecting pockets whose large surface forms a reservoirfor the fuel entering with little turbulence. After deflecting the flow,the fuel slowly enters actual tangential swirl channels 93 with lowturbulence, so a swirl that is largely free of interference can beachieved.

FIG. 8 shows an embodiment of a guide element 35. Over its outercircumference, guide element 35 has recesses 56 and tooth-shapedprojecting areas 98 in alternation. Tooth-shaped areas 98 may berounded. Guide element 35 is manufactured by punching, for example. Inthe example according to FIG. 8, bases 99 of the recesses are designedat an inclination, so that bases 99 of the recesses run perpendicular tothe axes of swirl channels 93 of swirl element 47 beneath them in anadvantageous manner.

1. A fuel injector for a fuel injection system of an internal combustionengine, comprising: an energizable actuating element; a valve needlethat is axially movable along a longitudinal axis of a valve; a fixedvalve seat; a valve seat element including an orifice followingdownstream from the fixed valve seat; a valve closing section arrangedon a downstream end of the valve needle and for working together withthe fixed valve seat for opening and closing the valve, wherein: thefixed valve seat is designed on the valve seat element; a flattened facerunning perpendicular to the longitudinal axis of the valve and beingarranged on the downstream end of the valve closing section downstreamfrom the fixed valve seat; a guide element including alternatingrecesses and tooth-shaped projecting areas along a periphery of theguide element, the recesses configured to channel fuel through the guideelement; and a swirl-producing element arranged upstream from the fixedvalve seat and downstream of the guide element, wherein: the flattenedface includes a diameter d that is greater than a diameter D of anoutlet orifice, and an entry plane of the outlet orifice is arrangedsuch that the entry plane is completely covered by a projection of theflattened face into the entry plane in a direction perpendicular to theflattened face.
 2. The fuel injector according to claim 1, wherein: thefuel injector is configured for a direct injection of a fuel into acombustion chamber of the internal combustion engine.
 3. The fuelinjector according to claim 1, wherein: a ratio of the diameter d of theflattened face to the diameter D of the outlet orifice is approximately1.5.
 4. The fuel injector according to claim 1, wherein: the valveclosing section includes a curved area that is at least partially one ofspherical and rounded, and the flattened face is adjacent to the curvedarea.
 5. The fuel injector according to claim 1, wherein: the valveclosing section includes a conical area that is at least partially atruncated conical taper in a downstream direction, and the flattenedface follows the conical area.
 6. The fuel injector according to claim1, wherein: the swirl-producing element includes a disk-shaped swirlelement directly upstream from the fixed valve seat.
 7. The fuelinjector according to claim 1, wherein: the outlet orifice is formed inthe valve seat element.
 8. The fuel injector according to claim 1,wherein the valve seat element includes a spray element which includesthe outlet orifice and is arranged downstream from the valve seat face.9. The fuel injector according to claim 6, wherein: the disk-shapedelement includes an inner opening area having a plurality of swirlchannels that extend completely over an entire axial thickness of thedisk-shaped swirl element, and the plurality of swirl channels is notconnected to an outer periphery of the disk-shaped swirl element by aperipheral edge area.
 10. The fuel injector according to claim 9,wherein: the inner opening area is formed by an inner swirl chamber andby the plurality of swirl channels opening into the inner swirl chamber.11. The fuel injector according to claim 10, wherein: the plurality ofswirl channels includes ends at a distance from the inner swirl chamber,and the ends as inlet pockets include a larger cross section than aremainder of the plurality of swirl channels.
 12. A fuel injector for afuel injection system of an internal combustion engine, comprising: anenergizable actuating element; a valve needle axially movable along alongitudinal axis of a valve; a fixed valve seat; a valve seat elementincluding an orifice following downstream from the fixed valve seat; avalve closing section arranged on a downstream end of the valve needleand arranged to work together with the fixed valve seat to open andclose the valve; wherein the fixed valve seat is arranged on the valveseat element; wherein a flattened face extends perpendicular to thelongitudinal axis of the valve and is arranged on the downstream end ofthe valve closing section downstream from the fixed valve seat; whereina guide element include alternating recesses and tooth-shaped projectingareas along a periphery of the guide element, the recesses configured tochannel fuel through the guide element; wherein a swirl-producingelement is arranged upstream from the fixed valve seat and downstream ofthe guide element; wherein the flattened face includes a diameter thatis greater than a diameter of an outlet orifice; and wherein aprojection of the flattened face in a direction perpendicular to theflattened face into an entry plane of the outlet orifice completelycovers the entry plane.